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Pounding Vs. Rolling Slabs


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#21 Biglou13

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Posted 19 July 2013 - 04:55 PM

 

this weekend warrior is interested.me too!

 

i found some info on the 'net  recently.... explaining warping  if piece is dried on flat surface,   top surface dries faster than bottom,  clay contracts as it dries causing warping,

 

 

me-   when dried between dry wall sheets  both surfaces dry more evenly,  cautious of edges drying faster i put in loose dry cleaner bag which is non absorbent and leaves the piece wet longerothers wax edges--- slows drying and more even drying---i weight the sandwich for good measure. how long do you leave it there?  do you move it to a drier piece of drywall as it dries?  if the object is to remove moisture would that not be better?

 

hypothesis--  with items that cannot be sandwiched, dry on ware board covered  and dry painfully slowly..  

 

not so much wet longer but  the key here is dry slower, and hopefully more even drying. bag is loose  with holes so there is some evaporation going on.  i leave it until its no longer cool to the touch, then dry on wire shelf.  its been humid so i have a thick piece going on 1.5 weeks.  smaller tile went one week. i check the piece occasionally flip, and flip dry wall the the non contact side is drier. if i had more pieces i would switch them out. I'm in no hurry. (i scrounged my dry wall for free,  from friends working on house).  i checked piece today  much drier than last time  edges drier than center,  but center still cool to touch.   sometimes ill put piece out for a few hours open,  flip and let sit for same time.   then back in sandwich and bag.....


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#22 weeble

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Posted 21 July 2013 - 05:02 AM

I often dry tiles in layered stacks of drywall, but then I'm not usually doing highly textured tiles, just rolled in plant stuffs.  I wrap the stack in plastic so the edge tiles don't dry too fast, then swap the damp drywall out with DRY drywall every day or so and let the wet stuff dry for tomorrow.  That way I can get away with firing the kiln in the same small room as I dry stuff.

 

One of these days the kiln MAY get a dedicated room, meanwhile everything is in one small room.


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#23 stephsteph

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Posted 21 July 2013 - 11:09 AM

pounding vs rolling. i think it depends on the clay and also the size of the slab. in most studio cases it will not make a difference, but when you begin to test the limits of the clay body you are using , with very large tiles for example, you may see a difference.

 

just as with throwing, cracking and warping occurs when there id a variation from  compression to tension..cracking occurs when there is an area that is stretched more (increases tension), warping occurs when there is an area of greater compression.

 

so the main thing is, whatever you do ,do it consistently. On large tiles where slabs are pounded (compressed) into a mold after being rolled out  or thrown(Stretched, tensioned), problems can occur where you pound  or compress one part of the tile more than another.

i worked in a RAM press tile shop for awhile and there was never a problem with warping or cracking even on very large pieces.

 

if you have a claybody that is problematic this is just one of many, many  factors that may affect   the outcome.

 

BTW..compressing clay rather than rolling it was the standard in architectural clay slab production, but the clay used for very large scale work is very different than the typical bagged  clay we purchase. It is very wet, so as to be maleable enough to slam into large molds and make large slabs,, but also has a higher grog content and is not very plastic.


Stephani Stephenson

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http://www.revivaltileworks.com

 


#24 LovesPurple

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Posted 26 July 2013 - 11:04 AM

I have both pounded out slabs for tiles, and rolled.  I did not see a difference.  I built myself a slab roller and it makes the whole process super easy and fast.  I dry my tiles between drywall boards.  I have a huge pile of them, and I put the damp tiles on new boards every day.  I also put weight on top of the pile of tiles between the drywall.  I found I end up with flatter tiles that way.



#25 Bob Coyle

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Posted 26 July 2013 - 12:57 PM

Speaking of tiles...

 

I made a set of 8 x 8 x 1/2 inch tiles for a table top. I followed all the instructions... flipped 90 deg and over after each roll...let the clay fall off the board rather than pulling it off... dried the clay for weeks between drywall... bisked and fired the tiles on clay wafers I made so that they would not be in contact with the shelves.

 

They still warped like hell! Asked around and everyone says I did everything correct. Any idea what went wrong?



#26 Biglou13

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Posted 26 July 2013 - 05:55 PM

bob my big tile is still drying  big for me 11 x 15 x 1/2 so nothing conclusive yet,     bob how did you transfer said tiles from roller to drying surface?   also i think some error may have entered at tile on clay wafer.   as stated above the silica or other high refractory between shelf and tile acts more like ball bearings as clay shrinks in firing.   if you re make     can you pound some.... finish on roller,    then   just roller some and see what the difference is, then fire some on silca or other high refractory, some one clay wafers,       

 

were clay wafers bisque fired also

 

until your post i was assuming it was the drying process that is major determining factor in warping. 


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#27 Bob Coyle

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Posted 26 July 2013 - 07:44 PM

I looked up several sites on the internet that talked about forming tiles.

 

One of the things they said was that lifting a tile off the bat that you roll it on can cause warping. So I rolled the tiles on a board then cut them then inverted the board onto the drywall and just let it flop off.

 

I then stacked the tiles and drywall sandwich so it was about five high and put a pound weight on top.

 

I let these dry for about three weeks ( in Santa Fe the humidity is about 15% if that)

 

I removed the tiles and placed each of them them on five per-fired clay disks about 3/4” wide and 3/16” thick. I fired them at the normal cone 5-6 firing I usually do.

They came out warped. Some worse than others. Didn't seem to have anything to do with kiln placement.

 

Maybe I need a much slower firing? I think I did everything else right



#28 Biglou13

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Posted 26 July 2013 - 08:51 PM

pictures of warped tiles?


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#29 oldlady

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Posted 26 July 2013 - 11:20 PM

there is a brand new segment of video of someone making tiles.  it is out today at the cad site.  i want to flip the clay he is working on and trim it better but that is why there are so many different ways of working.  check it out.

 

i put a post between bob coyle and big lou but it is not there.  did i miss that da&*_)^&   POST button again???

 

the question is are you putting these nicely flattened tiles on top of the disks as though they are feet at the corners?  i can see sagging like something in a hammock if that is the case.  lay the tiles flat or on a bed of sand or grog so they can slide around as they shrink.


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#30 Bob Coyle

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Posted 27 July 2013 - 12:35 PM

The tiles are supported with five buttons. four on the edges and one in the center.

 

Do you have a link address to the new video?



#31 LovesPurple

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Posted 29 July 2013 - 11:19 AM

I have done hundreds of tiles, big and small, and have had very little warpage.  I bisque fire them standing up in tile racks.  I glaze fire them with one small stilt under them, or stacked horizontally in tile racks.  Maybe it is your clay.  :rolleyes:



#32 perkolator

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Posted 29 July 2013 - 12:26 PM

For me it depends on how big of a slab I'm making and the intended purpose - but my opinions are slightly skewed since we usually do large-scale sculpture in our studio.  If it's just a slab of clay that is going to be added to something else or further manipulated (like made into a large hand-built cylinder) then I will just make by hand (pound and throw/stretch) or put it in a slab roller for speed because it doesn't really matter a whole lot.  I find that slab-rolled slabs tend to warp if not flipped over, or depending on how they were picked up, also depends on thickness.   You'd be amazed at how much warping you can achieve on a a 3/8" thick slab made on a roller without being flipped over when being made. very seldom do I use a slab roller for a slab smaller than 18"x18" - it's easier and faster to make smaller than this by hand.

 

If it's a structural slab that needs to stay flat, or a large slab (large slab for me is 24"x36" - same size as my large ware boards, and maybe 1-2" thick) then I will usually pound it by hand and sometimes roll it flat on the slab roller after I've done most of the work by hand to get rid of high-spots, but not always.  Usually for the largest slabs I will throw clay directly onto the plywood board in baseball-sized chunks, making sure they overlap.  Then I'll pound the hell out of it to even out the surface, sometimes walking on it barefooted or pounding with a 2x4.  To get an even surface, I'll first rake my fingernails across it in opposing directions, then a stiff rib tool in the same manner - usually works quite well as long as you go diagonal opposing directions.  I ALWAYS make sure to flip the slab over and compress from the other side - to flip a large slab, sandwich it with two boards, grab it tight and flip quickly (or with help).  If it's a large, thick slab that needs to stay flat, I will usually wrap the edges with plastic or even make a "frame" to build the slab in so the sides dry slower (since more surface are for air to wick away from corners = more prone to cracking on the sides), and the edges can get compressed using the frame as well.

 

I usually once-fire a lot of sculpture, so when firing large slabs like this I like to prop them up on a fields of 1" balls of kiln putty/wadding (equal parts silica, kaolin, grog) so that they stay flat and are evenly supported.  I suppose a bed of grog/sand would work but that'd only work on the base-level of a kiln stack for me unless it's all bisk.  sometimes we'll fire a large slab like this on edge, leaning against the bricks supporting the stack, only really warp if the slab was poorly constructed IMO.

 

I will definitely have to start experimenting with "dropping" a slab after it's made to reorient the particulates, to see if it makes any difference.  I recently learned about this and have never tried it before.  sounds like it makes some sense.



#33 Bob Coyle

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Posted 29 July 2013 - 01:27 PM

I have done hundreds of tiles, big and small, and have had very little warpage.  I bisque fire them standing up in tile racks.  I glaze fire them with one small stilt under them, or stacked horizontally in tile racks.  Maybe it is your clay.  :rolleyes:

Could be. I'm using MR-5 which is the same clay I use for throwing.



#34 Biglou13

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Posted 07 August 2013 - 04:42 PM

how does grog/ grit  (wedged into factory clays) factor into the warpage equation?  and does grit size have affect?


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